AUTHOR=Vijay Srinivasan , Hai Hoang T. , Thu Do D. A. , Johnson Errin , Pielach Anna , Phu Nguyen H. , Thwaites Guy E. , Thuong Nguyen T. T. 

TITLE=Ultrastructural Analysis of Cell Envelope and Accumulation of Lipid Inclusions in Clinical Mycobacterium tuberculosis Isolates from Sputum, Oxidative Stress, and Iron Deficiency

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02681

DOI=10.3389/fmicb.2017.02681

ISSN=1664-302X

ABSTRACT=<p><bold>Introduction:</bold> Mycobacteria have several unique cellular characteristics, such as multiple cell envelope layers, elongation at cell poles, asymmetric cell division, and accumulation of intracytoplasmic lipid inclusions, which contributes to their survival under stress conditions. However, the understanding of these characteristics in clinical <italic>Mycobacterium tuberculosis</italic> (<italic>M. tuberculosis</italic>) isolates and under host stress is limited. We previously reported the influence of host stress on the cell length distribution in a large set of clinical <italic>M. tuberculosis</italic> isolates (<italic>n</italic> = 158). Here, we investigate the influence of host stress on the cellular ultrastructure of few clinical <italic>M. tuberculosis</italic> isolates (<italic>n</italic> = 8) from that study. The purpose of this study is to further understand the influence of host stress on the cellular adaptations of clinical <italic>M. tuberculosis</italic> isolates.</p><p><bold>Methods:</bold> We selected few <italic>M. tuberculosis</italic> isolates (<italic>n</italic> = 8) for analyzing the cellular ultrastructure <italic>ex vivo</italic> in sputum and under <italic>in vitro</italic> stress conditions by transmission electron microscopy. The cellular adaptations of <italic>M. tuberculosis</italic> in sputum were correlated with the ultrastructure of antibiotic sensitive and resistant isolates in liquid culture, under oxidative stress, iron deficiency, and exposure to isoniazid.</p><p><bold>Results:</bold> In sputum, <italic>M. tuberculosis</italic> accumulated intracytoplasmic lipid inclusions. In liquid culture, clinical <italic>M. tuberculosis</italic> revealed isolate to isolate variation in the extent of intracytoplasmic lipid inclusions, which were absent in the laboratory strain H37Rv. Oxidative stress, iron deficiency, and exposure to isoniazid increased the accumulation of lipid inclusions and decreased the thickness of the cell envelope electron transparent layer in <italic>M. tuberculosis</italic> cells. Furthermore, intracytoplasmic compartments were observed in iron deficient cells.</p><p><bold>Conclusion:</bold> Our ultrastructural analysis has revealed significant influence of host stress on the cellular adaptations in clinical <italic>M. tuberculosis</italic> isolates. These adaptations may contribute to the survival of <italic>M. tuberculosis</italic> under host and antibiotic stress conditions. Variation in the cellular adaptations among clinical <italic>M. tuberculosis</italic> isolates may correlate with their ability to persist in tuberculosis patients during antibiotic treatment. These observations indicate the need for further analyzing these cellular adaptations in a large set of clinical <italic>M. tuberculosis</italic> isolates. This will help to determine the significance of these cellular adaptations in the tuberculosis treatment.</p>